This is CES 1991 Prototype #1:
Differences:
- Ring instead of Rings
- Different enemies
- No Lives counter
- HEX debug Sprite position on screen
YouTube Link
This is CES 1991 Prototype #2:
Differences:
- Ring instead of Rings
- Lives counter working
- Life monitor on the top of the loop
YouTube Link
The last known footage Sonic 1 Prototype #3:
Differences:
- Rings now writen
- Boss with rotating ball
YouTube Link
Please read the video description (on youtube) of each video.